College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA
Routine whole body radiographs are a common component of many avian diagnostic patient evaluations, and are used to help rule in or rule out different problems on an initial differential diagnoses list. This presentation will include a review of diagnostic-quality survey and contrast radiographs and normal radiographic anatomy (using a parrot model). A review of common problems seen radiographically will be illustrated using clinical case presentations.
Technique and Positioning
Ideally, radiographic units used for avian imaging should include specifications for at least 300 mA (milliamps), 40–90 kVp (kilovolt peak) settings, and minimum exposure time < 1/60 second (to minimize motion artifact due to rapid respirations or muscle tremors). Technique charts based upon four to six sizes of avian patients (ranging from a 30 g budgerigar to a 1500 g macaw) should be developed in each veterinary hospital, using the specific radiographic equipment and film-screen combinations or digital radiology system available. The same settings are generally used for both lateral and ventral dorsal views in birds.
Ideally, both lateral and ventral dorsal (VD) views should be taken for all avian radiographs. Table top, nongrid technique using a clear Plexiglas board is helpful for properly positioning awake or anesthetized (preferred) patients. Use of isoflurane anesthesia via mask induction is ideal for short procedures and results in better quality radiographs (improved positioning and less motion artifact), less stress for the patient, and reduced radiation exposure potential for personnel. Manual restraint can be used too, and both techniques will be shown in the presentation. Masking tape can be safely used to tape the wings, legs and neck in proper position. A bird properly positioned in lateral view will have both wings fully extended dorsally, the head and neck stretched, both legs pulled caudally as much as possible, and the shoulders (coracoids, clavicle and scapula bones) and acetabula are superimposed. If separate lateral views of the legs are desired, they can be split; otherwise, the author prefers to have a less-obstructed view of the mid and caudal coelomic cavity when both legs are extended caudally.
A bird is properly positioned in VD view when the keel and spine are superimposed, the head and neck are extended, the wings are extended from the shoulders out to each side (okay if the elbows are carpi are flexed to keep the entire wing in one view if desired), and the legs are extended caudally. Slight deviations in positioning in either view may still result in acceptable diagnostic films, but severely excessive rotational views should be retaken.
Normal Radiographic Anatomy
Practitioners who are learning avian radiology are encouraged to do some necropsies on birds from which radiographs were taken in order to get the 3-dimensional view of avian anatomy. Knowing normal avian anatomy from necropsies is helpful for learning normal (and abnormal) radiographic anatomy.2 It also helps to have resources to consult1,3-4, both during the steep learning phase, as well as when atypical cases are presented. Although there are many anatomic variations between different species of birds, the basic structures are generally identifiable across taxonomic groups.
Ventral-Dorsal View of Parrot Radiographs
Interpretation of normal organ size and location in parrots may not apply directly to other groups of birds, such as raptors, waterfowl, and poultry species. In parrots, the junction between the heart and liver silhouette has an "hour-glass" shape. The width of this "cardio-hepatic waist" can be used as a guideline for assessing liver enlargement, but this general rule does not apply to raptors, for example, in which the cardio-hepatic waist has a much wider and poorly defined junction between the heart and liver. Another tool for assessing liver size is to draw a pair of imaginary parallel lines between the scapula and acetabula. Extension of the lateral edges of the liver beyond these lines may be indicative of hepatomegaly, as long as the VD position is correct (keel and spine are superimposed). Also, since the proventriculus is superimposed on the left side of the liver, any proventricular enlargement (i.e., due to disease that can cause proventricular dilation, or due to a full GI tract) can result in unilateral widening of the liver in that location. Lastly, a large mass in the caudal coelomic cavity can cranially displace organs, which might give the liver lobes the appearance of being wider than normal.
Without GI contrast agents, visualization of the gastrointestinal tract is somewhat limited on the VD view. The crop is usually not visible unless there is air or ingesta present. Likewise, unless the proventriculus is dilated or filled with ingesta, it is mostly superimposed on the left lobe of the liver. The ventriculus is a very muscular organ and is often visible on the left side of the spine between the acetabula. Presence of mineralized grit (or heavy metal fragments!) within the ventriculus facilitates identification on a VD radiograph. Although not entirely symmetrical, the cranial and caudal thoracic and abdominal airsacs should be visible on both sides of the intracoelomic organs. Other organs such as lungs, spleen, kidney and gonads are best assessed on the lateral view.
Lateral View of Parrot Radiographs
This view is most useful for assessing the lungs, coelomic airsacs, heart, liver, proventriculus, ventriculus, small intestines, spleen, and kidneys/gonad. The parabronchi openings can be viewed (with a honey comb appearance with fine detail film in normal birds) and granulomas may be visualized within the lungs on lateral view. General rules for assessing liver size can also be applied to the lateral view in parrots. In adult birds with a normal size liver, the caudal border does not extend beyond the keel (liver size may be larger, relative to the keel, in juvenile parrots). The radiolucent "triangle" composed of the dorsal mid-coelomic airsacs is another useful feature in parrots to use for assessing organ size and displacement. This space is outlined by the caudal border of the lungs, the dorsal border of the proventriculus, the cranial border of the small intestines, and the ventral-cranial border of the kidney/gonad area. A decrease in space in this lucent area can result from 1) hepatic enlargement displacing the proventriculus dorsally; 2) proventricular or splenic enlargement, expanding dorsally into this space; 3)gonad or renal enlargement, expanding ventral-cranially into this space; and 4) caudal intracoelomic mass enlargement displacing small intestines cranially (i.e., retained egg, chronic salpingitis and oviduct enlargement, granuloma, etc.).
The proventriculus is relatively easy to see on the lateral view, located dorsally to the liver. The ventriculus generally lies just dorsal to the ventral body wall, and directly ventral to the acetabula. As in the VD view, if mineralized grit or metal are present in the ventriculus, its location is clearly defined. The normal sized spleen is not always visible on the lateral view (except in most macaws), and when visible, is dorsal to the caudal proventriculus near the junction with the ventriculus. The cranial division of the avian kidney is most readily viewed on lateral radiographs, and the gonads are located cranial to this portion of the avian kidney (however, the gonads are usually not visible as a distinct organ unless there is neoplastic gonadal enlargement or perhaps many large follicles on an ovary).
Clinical case examples of parrots with trauma or diseases of the liver, gastrointestinal, respiratory, and reproductive tracts will be used to illustrate the valuable benefit of radiology for diagnostic evaluation.
1. Krautwald-Junghanns ME, Pees M. Imaging techniques. In: Tully TN, Dorrestein GM, Jones AK, eds. Handbook of Avian Medicine. 2nd ed. Philadelphia, PA: Saunders/Elsevier; 2009:85–100.
2. McLelland J. A Color Atlas of Avian Anatomy. Philadelphia, PA: Saunders; 1991.
3. Naldo J. Radiography. In: Samour J, ed. Avian Medicine. 2nd ed. Philadelphia, PA: Mosby/Elsevier; 2008:79–96.
4. Silverman S, Tell LA. Radiology of Birds: An Atlas of Normal Anatomy and Positioning. St. Louis, MO: Saunders/Elsevier; 2010.